1. The metadata necessary to construct the frontend markup and state myself, using javascript or even a process on a remote server. For example, form information (id, name, is_valid, post_url), field information (collection of fields, each with e.g. name, type, label, order, placeholder_value, current_value, validation_strategy, is_valid, error_message). In short, all of the information about a form and its state, decoupled from markup.

4. I mean "responsive" in the technical Web development sense; using the same markup for intelligent adaptation to different screen dimensions and resolutions through the use of a grid system and media queries. Responsive frameworks include Bootstrap (http://getbootstrap.com/) and Foundation (http://foundation.zurb.com/). From my research I did not conclude that SoSci Survey was responsive in this sense.

Another way to pose my question might be, "how can I create a SoSci Survey frontend using Bootstrap or Foundation?"

ad 1) Well, JS provides this information about any HTML form anyway. However, the form will be processed "at once", i.e., submission of single inputs is valid only for some special inputs ("internal variables" with live transmission). What would be the added value if another JS object repeated the information that is available by default (and through the DOM's standards)?

PS: To create custom inputs like, e.g., sliders, SoSci Survey just hides the original inputs (that serve as fallback for people disabling JavaScript or working with a Braille line) and creates the JavaScipt-enhanced input below, which writes it's results back into the old-school HTML inputs.